The present invention relates generally to voltage level shifter circuitry, and more specifically to level shifter circuitry with low current.
Level shifter circuitry is utilized in a variety of applications typically to amplify an output signal to a desired voltage swing level. For instance, level shifter circuitry is often utilized as a stage in crystal oscillator circuitry to amplify and therefore convert a small sine-wave form signal to a fully swinged digital square wave form. Referring to FIG. 1, a prior art oscillator circuit having an Oscillator, a Voltage Regulator, an Amplifier/Level Shifter stage, and an Output stage which produces an Output signal is shown. The Oscillator, Voltage Regulator, and Output stage are provided with supply voltage Vcc; the Voltage Regulator provides the Amplifier/Level Shifter stage with supply voltage Vcc1, as shown. The Voltage Regulator is used to lower the power supply level of the Amplifier/Level Shifter stage such that the total current utilized by the oscillator circuit is reduced. The Output stage is used to get a fully swinged digital Output signal. The current in the Output stage is Vcc dependent. Thus, the use of a single Voltage Regulator element of the type shown in FIG. 1 may not be a good approach for lowering the current consumption of the oscillator circuitry over a wide range of supply voltage, such as Vcc.
Additionally, the oscillator circuitry of FIG. 1 presents a noise immunity problem. A single signal which is generated by the Oscillator is used as the input signal of the Amplifier/Level Shifter stage. Since the wave form generated by the Oscillator is normally a sine-wave form, it is very easy and common for noise from other parts of a system having the oscillator circuitry, through the common ground bus or substrate of the system, to interfere with the sine-wave form. This interference may manifest itself as a glitch which could accidentally trigger the Amplifier/Level Shifter stage, thereby causing unstable frequency response.
Thus, there exists an unmet need in the art to provide level shifter circuitry capable of stable frequency response and low current consumption over a wide range of supply voltage.